There are known techniques for measuring CD's using a scanning electron microscope (CD-SEM); a scanning probe microscope (CD-SPM) such as described in commonly owned U.S. Pat. No. 6,445,453 (ZI-14) entitled “Scanning Interferometric Near-Field Confocal Microscopy” by Henry A. Hill, the contents of which are herein incorporated in their entirety by reference; and a scanning optical microscopy (CD-SOM) based on images of features. There are also known techniques for measuring the profile of a surface by the use of different forms of linear displacement interferometric metrology such as based on white light interferometric techniques and there are known techniques for measuring properties of a surface for example using differential confocal microscopy.